I used to fly America West out of SNA almost exclusively.
Of course, that was back when they had a great elite program and hadn't joined US. Service, prices, and elite benefits are now much worse.
But two big pluses remain. Two of US's hubs are less than an hour flight away: Las Vegas and Phoenix. And from those two hubs there are many direct flights to cities covering the entire country.
And finally, US still has the only direct flights to Vegas.